Most of you have probably heard a story that gets passed around of some old maintenance man, or factory worker, who kept all his notes on paper or was the only one keeping a thing running.
After he leaves, maybe with some abuse, the machine breaks down and the company is losing lots of money. He comes back and charges a fortune, then fixes it unexpected quickly and simply. The old boss is indignant and we get a lesson about being an expert.
Well, anyway, that story is often spun up into being hot garbage. The old guy who maintained the machine is not valuable or smart for being irreplaceable, he is a victim of having his expertise undervalued for many years. He is probably a specialist in a technology that is being, like him, phased out. Businesses should not tell this story like it was a good thing.